Digital imaging has been adapted to serve dentistry for both diagnostic and cosmetic purposes. For example, there have been a number of dental imaging systems developed for diagnosis of dental caries in its various stages, capable of assisting in this diagnostic task without the use of x-rays or other ionizing radiation. One method that has been commercialized employs fluorescence, caused when teeth are illuminated with high intensity blue light. This technique, termed Light-Induced Fluorescence (LIF), operates on the principle that sound, healthy tooth tissue yields a higher intensity of fluorescence under excitation from some wavelengths than does de-mineralized tooth tissue that has been damaged by caries infection. The strong correlation between mineral loss and loss of fluorescence for blue light excitation is then used to identify and assess carious areas of the tooth. A different relationship has been found for red light excitation, a region of the spectrum for which bacteria and bacterial by-products in carious regions absorb and fluoresce more pronouncedly than do healthy areas. Utilizing this behavior, U.S. Pat. No. 4,290,433 entitled “Method and Apparatus for Detecting the Presence of Caries in Teeth Using Visible Luminescence” to Alfano discloses a method to detect caries by comparing the excited luminescence in two wavelengths. The use of fluorescence effects for caries detection is also described in U.S. Pat. No. 6,231,338 entitled “Method and Apparatus for the Detection of Carious Activity of a Carious Lesion in a Tooth” to de Josselin de Jong et al.
Reflectance characteristics of visible light have also been used for oral caries diagnosis. For example, U.S. Pat. No. 4,479,499 entitled “Method and Apparatus for Detecting the Presence of Caries in Teeth Using Visible Light” to Alfano describes a method to detect caries by comparing the intensity of the light scattered at two different wavelengths. Commonly assigned U.S. Patent Application Publication 2007/0099148, previously mentioned, describes an improved method for caries detection that combines both fluorescence and reflectance effects.
Among commercialized products for diagnostic dental imaging using fluorescence behavior is the QLF Clinical System from Inspektor Research Systems BV, Amsterdam, The Netherlands, described in U.S. Pat. No. 6,231,338. Using a different approach, the Diagnodent Laser Caries Detection Aid from KaVo Dental GmbH, Biberach, Germany, described in U.S. Pat. No. 6,024,562, detects caries activity monitoring the intensity of fluorescence of bacterial by-products under illumination from red light. Other commercial products, such as the DIFOTI system from Electro-Optical Sciences, Irvington, N.Y., described in U.S. Pat. No. 6,672,868, use transmission of light through the tooth structure for diagnostic imaging.
Diagnostic imaging methods have been developed for use with hand-held devices. For example, U.S. Patent Application Publication 2005/0003323, entitled “Diagnostic Imaging Apparatus” by Naoki Katsuda et al. describes a complex hand-held imaging apparatus suitable for medical or dental applications, using fluorescence and reflectance imaging. The '3323 Katsuda et al. disclosure shows an apparatus that receives the reflection light from the diagnostic object and/or the fluorescence of the diagnostic object with different light irradiation. However, with such an approach, any unwanted specular reflection produces false positive results in reflectance imaging. Moreover, with the various illumination embodiments disclosed, the illumination directed toward a tooth or other diagnostic object is not uniform, since the light source is in close proximity to the diagnostic object.
Cosmetic dentistry has also taken advantage of digital imaging capability to some extent, primarily for shade-matching in tooth restoration or replacement. There have been numerous solutions proposed for providing some form of automated shade matching to assist the dentist. A few examples are given in U.S. Pat. Nos. 6,132,210 and 6,305,933, both entitled “Tooth Shade Analyzer System and Methods” both to Lehmann; and in U.S. Patent Application Publication No. 2005/0074718 entitled “Tooth Shade Scan System and Method” to Graham et al. Apparatus solutions for cosmetic imaging are outlined, for example, in International Publication No. WO2005/080929 entitled “Equipment and Method for Measuring Dental Shade” by Inglese and in U.S. Pat. No. 4,881,811 entitled “Remote Color Measurement Device” to O'Brien. Commercialized hand-held products directed to shade matching include the ShadeScan™ system from Cynovad, Montreal, Calif., described in Cynovad brochure 1019 of February 2002; and the Shade-Rite™ Dental Vision System from X-Rite Inc., Grandville, Mich., described in U.S. Pat. No. 7,030,986. Notably, hand-held shade-matching systems are not designed for ease of access to any but the front teeth. Conventional shade-matching techniques can match tooth color acceptably, but may not provide enough data for providing a substitute tooth that appears real and exhibits some amount of translucence. This is largely because conventional cosmetic imaging systems are directed primarily to color matching, but provide insufficient information on tooth translucency and surface texture. For cosmetic systems that measure translucency, little or no attention is paid to uniformity of illumination. This results in an uneven distribution of light and reduces the overall accuracy of the system for measuring tooth translucency.
In spite of the growing range of imaging devices that is now available to the dental practitioner for diagnostic and cosmetic purposes, there is still room for improvement. Diagnostic imaging apparatus and shade-matching systems are still separate pieces of equipment, each system having its own requirements for system optics. To a large extent, this is the result of their different functions, affecting numerous components from illumination, light shaping, and imaging subsystems. For example, the illumination requirements for diagnostic imaging, largely using fluorescence effects, differ significantly from those of cosmetic imaging, which largely employs reflective light. Specular reflection can be undesirable for both diagnostic and cosmetic imaging, but must be compensated in different ways for each type of imaging. Image sensing, the use of polarization and spectral content, and other features further differentiate diagnostic from cosmetic systems. Thus, it would be advantageous to provide an intra-oral camera that could be used for both diagnostic and cosmetic functions.